This invention generally relates to touch actuated capacitance type switches. More particularly, this invention relates to such switches wherein the areas which are touched to initiate actions are formed from a metallic conductive film that has a low degree of abrasion resistance. Still more specifically, this invention relates to such a switch wherein the conductive films are given a protective overcoat to prevent abrasion damage to them.
The use of touch panels as switches has become increasingly common in household appliances. In particular, such panels have proven popular in microwave ovens. One problem with such panels is their cost. The front surface, where the touch sites are located, must be able to withstand cleaning by harsh, abrasive household cleaners. The only material to date which has proven usable for such panels is NECCA or Electropane, tradenames for tin oxide coated plate glass. Such glass is quite expensive in initial cost and creates further costs in processing since all of the tin oxide coating must be etched off except for the areas where the touch sites are to be located. This is a wasteful process. In addition, the backs of such switches are typically coated, for decorative purposes and to lay down the other side of a capacitor, with epoxy inks. Such inks are difficult to handle and have short pot lives, further adding to the manufacturing costs. I have found that discrete sites or pads of a conductive material may be placed on the front of a touch switch. This avoids the necessity of etching away portions of an overall conductive coating as in the past. However, such discrete sites of conductive material are quite sensitive to abrasion damage. I have found that they may be adequately protected without degrading performance by overcoating them with an open pattern of an abrasion resistant material. Further, the back face coating and rear conductive sites may be put on using an organopolysiloxane material which avoids the problems of using epoxy inks.